Automatic dishwashing, particularly in domestic appliances, is an art very different from fabric laundering. Domestic fabric laundering is normally done in purpose-built machines having a tumbling action. These are very different from spray-action domestic automatic dishwashing appliances. The spray action in the latter tends to cause foam. Foam can easily overflow the low sills of domestic dishwashers and slow down the spray action, which in turn reduces the cleaning action. Thus in the distinct field of domestic machine dishwashing, the use of common foam-producing laundry detergent surfactants is normally restricted. These aspects are but a brief illustration of the unique formulation constraints in the domestic dishwashing field.
Automatic dishwashing with bleaching chemicals is different from fabric bleaching. In automatic dishwashing, use of bleaching chemicals involves promotion of soil removal from dishes, though soil bleaching may also occur. Additionally, soil antiredeposition and anti-spotting effects from bleaching chemicals would be desirable. Some bleaching chemicals, (such as a hydrogen peroxide source, alone or together with tetraacetylethylenediamine, TAED) can, in certain circumstances, be helpful for cleaning dishware, but this technology gives far from satisfactory results in a dishwashing context: for example, ability to remove tough tea stains is limited, especially in hard water, and requires rather large amounts of bleach. Other bleach activators developed for laundry use can even give negative effects, such as creating unsightly deposits, when put into an automatic dishwashing product, especially when they have overly low solubility. Other bleach systems can damage items unique to dishwashing, such as silverware, aluminium cookware or certain plastics.
Consumer glasses, dishware and flatware, especially decorative pieces, as washed in domestic automatic dishwashing appliances, are often susceptible to damage and can be expensive to replace. Typically, consumers dislike having to separate finer pieces and would prefer the convenience and simplicity of being able to combine all their tableware and cooking utensils into a single, automatic washing operation. Yet doing this as a matter of routine has not yet been achieved.
On account of the foregoing technical constraints as well as consumer needs and demands, automatic dishwashing detergent (ADD) compositions are undergoing continual change and improvement. Moreover environmental factors such as the restriction of phosphate, the desirability of providing ever-better cleaning results with less product, providing less thermal energy, and less water to assist the washing process, have all driven the need for improved ADD compositions.
A recognized need in ADD compositions is to have present one or more ingredients which improve the removal of hot beverage stains (e.g., tea, coffee, cocoa, etc.) from consumer articles. Strong alkalis like sodium hydroxide, bleaches such as hypochlorite, builders such as phosphates and the like can help in varying degrees but all can also be damaging to, or leave a film upon, glasses, dishware or silverware. Accordingly, milder ADD compositions have been developed. These make use of a source of hydrogen peroxide, optionally with a bleach activator such as TAED, as noted. Further, enzymes such as commercial amylolytic enzymes (e.g., TERMAMYL.RTM. available from Novo Nordisk S/A) can be added. The alpha-amylase component provides at least some benefit in the starchy soil removal properties of the ADD. ADD's containing amylases typically can deliver a somewhat more moderate wash pH in use and can remove starchy soils while avoiding delivering large weight equivalents of sodium hydroxide on a per-gram-of-product basis. It would therefore be highly desirable to secure improved bleach activators specifically designed to be compatible in ADD formulations, especially with enzymes such as amylases. A need likewise exists to secure better amylase action in the presence of bleach activators.
Certain manganese catalyst-containing machine dishwashing compositions are described in U.S. Pat. No. 5,246,612, issued Sep. 21, 1993, to Van Dijk et al. The compositions are said to be chlorine bleach-free machine dishwashing compositions comprising amylase and a manganese catalyst (in the +3 or +4 oxidation state), as defined by the structure given therein. Preferred manganese catalyst therein is a dinuclear manganese, macrocyclic ligand-containing molecule said to be Mn.sup.IV.sub.2 (u-O).sub.3 (1,4,7-trimethyl-1,4,7-triazacyclononane).sub.2 (PF.sub.6).sub.2. Such catalyst materials which contain these more complicated ligands typically will require several synthesis steps to produce, thereby driving up the cost of the catalysts and making them less likely to be readily available for use. Thus, there continues to be a need for simple, widely available catalysts that are effective in automatic dishwashing compositions and methods.
The simple cobalt catalysts useful herein have been described for use in bleach-containing laundry compositions to wash stained fabrics as taught by U.S. Pat. No. 4,810,410, to Diakun et al, issued Mar. 7, 1989. For example, Table 8 therein provides the stain removal results for a series of stains on fabrics washed with laundry compositions with and without the cobalt catalyst [Co(NH.sub.3).sub.5 Cl]Cl.sub.2. Tea stain removal from fabrics as reported therein appears marginal at best by comparison to the other stains measured.
The comparative inferiority of the cobalt catalysts herein for laundry applications to remove tea stains is reinforced by the teachings contained in the later filed European Patent Application, Publication No. 408,131, published Jan. 16, 1991 by Unilever NV. Example IV therein, said to be a comparison of the cobalt-cobalt complexes which are viewed as the invention of that application versus the "[Co(NH.sub.3).sub.5 Cl]Cl.sub.2 of the art" (referring to the earlier publication of the European equivalent of the above-noted Diakun et al patent), reports values for removal of tea stain as follows: Co--Co (26.3); [Co(NH.sub.3).sub.5 Cl]Cl.sub.2 (20.6), which is lower than that observed for a simple Mn+2 catalyst as reported in Example II (having a tea stain removal value of 21.4).
Similar results for manganese catalysts versus cobalt catalysts are reported for laundry uses to remove tea stains from cotton fabrics in U.S. Pat. No. 5,244,594, to Favre et al., issued Sep. 14, 1993. Therein, Example I provides data slowing a Co--Co catalyst according to EP 408,131 is inferior to the manganese catalysts. Further, Example IV also reports lower stain removal at 20.degree. C. for a Co--Co catalyst of EP 408,131 and the [Co(NH.sub.3).sub.5 Cl]Cl.sub.2 catalyst of the Diakun patent versus a manganese catalyst.
While such inferior results are seen for removal of tea stain from fabrics during laundry processes, when used in automatic dishwashing compositions according to the present invention, these catalysts provide surprisingly effective tea stain removal from dishes. Such effectiveness would not have been expected from the prior art.
It is an object of the instant invention to provide automatic dishwashing compositions, especially compact granular, phosphate-free and chlorine bleach-free types, incorporating an improved selection of cobalt catalyst-containing bleaching ingredients. A further object is to provide fully-formulated ADD compositions with or without amylase enzymes, but especially the former, wherein specific cobalt catalyst-containing bleach systems are combined with additional selected ingredients including conventional amylases or bleach-stable amylases, so as to deliver superior tea cleaning results and at the same time excellent care for consumer tableware and flatware.